Mobile communication technologies are widely used today with mobile networks. A mobile network may include a number of cells, each corresponding to a geographical area. Within each cell, communication terminals such as mobile phones or, more generally, user equipment (UE), access network services such as phone services or Internet services, data streaming, etc., through an interface station such as a base station.
Mobile communication technologies have evolved through several generations. As an example, second generation (2G) technologies include Global System for Mobile Communications (GSM), and third generation (3G) technologies include Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) and Wideband Code Division Multiple Access (WCDMA). More recently, Long Term Evolution (LTE) emerged as one of the next generation wireless communication standards, as an evolution from 3G technologies.
Siemens and China Academy of Telecommunications Technology (CATT) first developed TD-SCDMA, which is one of the five International Mobile Telecommunications-2000 (IMT-2000) standards accepted by the International Telecommunication Union (ITU) and adopted by the 3rd Generation Partnership Project (3GPP). TD-SCDMA is a TDMA/TDD system with an adaptive CDMA component operating in synchronous mode and provides both symmetric circuit-switched services (such as speech or video) as well as asymmetric packet-switched services (such as mobile Internet access). TD-SCDMA uses Time Division Duplex (TDD), in contrast to the FDD used by WCDMA. In a TD-SCDMA system, a radio sub-frame includes 7 general time slots and 3 special time slots. The 7 general time slots are referred to as timeslot 0 (TS0) to timeslot 6 (TS6), in which TS0 is a downlink time slot, TS1 is an uplink time slot, and the remaining general time slots can be dynamically configured as either downlink or uplink time slots.
In a TD-SCDMA system, the base stations, or Node Bs, directly communicate with communication terminals, and a radio network controller (RNC) controls operations of Node Bs.
In an LTE system, the base stations are referred to as eNode Bs. In an LTE system, the base stations directly communicate with communication terminals without a separate controller such as the RNC. An LTE system can implement either Time Division Duplex (TDD) or Frequency Division Duplex (FDD). In TDD LIE, communications in two opposite directions between the base station and mobile phones occur in the same frequency band but different time slots. In FDD LTE, communications in two opposite directions between the base station and mobile phones occur at the same time but in different frequency bands.
A communication terminal may move across a wide geographical area where multiple generations of communication technologies, such as GSM, TD-SCDMA, and LTE, may co-exist, and different parts of the geographical area may have different technological coverage. To obtain best network coverage, therefore, communication terminals are often dual-mode or multi-mode. For example, a dual-mode terminal may operate on an LTE network in most places, but would switch to a GSM network when the terminal moves into an area where LTE coverage is not available. As another example, a dual-mode terminal may support both 3G TD-SCDMA and 2G GSM technologies. A multi-mode terminal may support GSM, TD-SCDMA, and LTE. A dual-mode or multi-mode terminal enables communication through, for example, a slower 2G GSM network, when 3G or LTE is not available.
In an area where networks of different modes coexist, a communication terminal operating in one particular mode may measure other supported modes in preparation for a handover to another mode should the current mode become less desirable. Such handover is sometimes referred to as the inter-Radio Access Technology (inter-RAT) handover, and such measurement the inter-RAT measurement. Standard documents, such as 3GPP standards, often specify the circumstances under which a communication terminal should perform inter-RAT measurements.
In inter-RAT measurements, a communication terminal measures signals transmitted by another network to determine the signal strength, network capacity, etc., of such other network, referred to herein as the target network. Based on the measurements, the communication terminal or the network that the communication terminal currently communicates with—also referred to herein as the current network—may then determine whether the terminal should handover to the other network. To gain sufficient knowledge of the target network, the communication terminal may need to measure different signals transmitted in different frames of the target network.
When the current network and the target network operate with different radio frame structures with different frame periods, the communication terminal can often successfully measure different signals form the target network with sufficiently long measurement periods. As an example, a communication terminal communicating with a TD-SCDMA network can measure a GSM network during idle time slots of the TD-SCDMA network. As long as the measurement time is sufficient, the communication terminal can always measure a particular signal, such as a pilot signal, reference signal, or broadcast signal, that periodically appears at a particular frame position of the GSM network, because the time slot that the particular signal appears in the GSM network will eventually align with an the time slot in the TD-SCDMA network.
Inter-RAT measurement, however, cannot be easily performed when the time period of the radio frames of two different radio access systems are the same. As an example, a TDD-LTE system and a TD-SCDMA system have radio frames with the same period, i.e., 5 ms. A communication terminal operating in a TDD-LTE network may not be able to measure a particular signal of a TD-SCDMA network if the radio frame where the particular signal appears is not aligned with an idle time slot in the TDD-LTE network, and such misalignment will not change over time.
To mitigate this problem in a dual-mode terminal that supports TDD-LTE and TD-SCDMA, the concept of measurement occasion in TD-SCDMA was introduced. Specifically, the current network in communication with the terminal configures measurement occasions, during which neither the base station nor the communication terminal transmits data to each other.
In the TD-SCDMA system, measurement occasions are configured using either information element (IE) “CELL_DCH measurement occasion info LCR” or IE “Idle Interval Information.” CELL_DCH refers to a state in a Radio Resource Control (RRC) connected mode. In an RRC connected mode, as opposed to an RRC idle mode, a communication terminal is usually engaging in communication services, such as telephone calls, with the network. The CELL_DCH state is one of the protocol states in the RRC connected mode that allocate a dedicate channel (i.e., DCH) for the communication terminal. LCR stands for low chip rate and refers to one of the two transmission modes (the other being HCR, i.e., high chip rate) specified in the 3GPP UMTS-TDD (Universal Mobile Telecommunication System—time division duplexing) standard. The HCR transmission mode has a higher speed than the LCR transmission mode. LCR is sometimes also regarded as an abbreviation of the TD-SCDMA in the 3GPP protocol. Detailed information may be found in the 3GPP Technical Specification 25.331, v9.9.0.
IE “CELL_DCH measurement occasion info LCR” can be configured in many controlling signals in a TD-SCDMA system, including, for example, a Radio Bearer Control message, a Cell Update Confirm message, or a Measurement Control message. IE “CELL_DCH measurement occasion info LCR” includes parameters such as Measurement Purpose, Status Flag, Timeslot Bitmap, k (hereinafter referred to as k1), Offset (hereinafter referred to as Offset1), and M_Length.
The Measurement Purpose parameter indicates the measurement purpose of the corresponding measurement occasion, such as whether the purpose is for an inter-frequency measurement of a TD-SCDMA system, a measurement of a GSM system, a measurement of an LTE system, or a combination thereof. In particular, the Measurement Purpose parameter may indicate any one of or any combination of the following five measurements: a TD-SCDMA inter-frequency measurement, a GSM carrier RSSI (Received Signal Strength Indicator), an initial BSIC (Base Station Identity Code) identification, a BSIC re-confirmation, and an E-UTRA measurement (i.e., an LTE measurement).
The Status Flag parameter indicates whether a measurement occasion pattern sequence shall be activated or deactivated. In particular, the Status Flag includes a range of enumerated values indicating whether the corresponding measurement occasion is in an activated state or a deactivated state.
The Timeslot Bitmap parameter indicates which of the time slots are allocated for measurement. In a Timeslot Bitmap, for example, Bit 0 is for timeslot 0, Bit 1 is for timeslot 1, Bit 2 is for timeslot 2, and so forth. Any bit with a value 0 may indicate that the corresponding timeslot is not used for measurement. And any bit with a value 1 may indicate that the corresponding timeslot is used for measurement.
The k1, Offset1, and M_Length parameters are used in the calculation of CELL_DCH measurement occasion. Under the RRC protocol, in a CELL-DCH state, when CELL_DCH measurement occasion pattern sequence(s) is (are) configured and activated for some specified measurement purposes, a communication terminal shall perform corresponding measurements during the timeslot(s) indicated by Timeslot Bitmap within a time period from frame SFNstart to frame SFNstart+M_Length−1. SFN refers to System Frame Number in a TD-SCDMA system, and the SFNstart can be determined by equation A as follows.SFNstart mod(2k1)=Offset1  Equation A.In equation A, k1 is CELL_DCH measurement occasion cycle length coefficient; the actual measurement occasion period equals to 2k1 radio frames; Offset1 is the measurement occasion position in the measurement period; M_Length is the actual measurement occasion length in frames starting from Offset1; and Mod is the modulo calculation.
In IE “CELL_DCH measurement occasion info LCR,” the value of k1 can be from 1 to 9; the value of Offset1 can be from 0 to 511; and the value of M_Length can be from 1 to 512. For example, according to equation A, if k1=2, Offset1=0. M_Length=1, and Timeslot Bitmap indicates timeslot 4, then the communication terminal can perform the measurement corresponding to the Measurement Purpose within timeslot 4 in a frame that has a length of 1 radio frame, when SFN is in multiples of 4 (i.e., 0, 4, 8, and so forth).
As described above, in a TD-SCDMA system, measurement occasions can also be configured using IE “Idle Interval Information.” IE “Idle Interval Information” includes two parameters: a coefficient parameter k (hereinafter referred to as k2) and Offset (hereinafter referred to as Offset2). Under Section 8.6.7.25 of the RRC protocol, if a communication terminal receives IE “Idle Interval Information,” it shall store this IE and execute inter-RAT measurements, if needed, during an idle interval in System Frame Number (SFN) determined by Equation B below.Offset2=SFN mod(2k2).  Equation B.In equation B, k2 is an coefficient parameter to calculate the idle interval period, and Offset2 is the idle interval position in a single period. The value of k2 can be from 2 to 3 and the value of Offset2 can be from 0 to 7.
According to Equation B. IE “Idle Interval Information” can configure 1 frame in every 4 or 8 frames to be a measurement occasion, during which an inter-RAT measurement can be performed. On the other hand, as described above, IE “CELL_DCH measurement occasion info LCR” can be configured so that the communication terminal may execute a particular measurement during a specified time slot that periodically appears in multiple frames. That is, IE “Idle Interval Information” configures the measurement occasion using a frame as a unit, while IE “CELL_DCH measurement occasion info LCR” configures the measurement occasion using a time slot as a unit.
Because the measurement purpose of IE “Idle Interval Information” is inter-RAT measurement, IE “Idle Interval Information” is included in IE “Inter-RAT measurement” And according to the 3GPP specification, IE “Inter-RAT measurement” is included in the “Measurement Control” information message, which is sent from the network to a communication terminal to setup, modify or release a measurement. Besides IE “Inter-RAT measurement,” the “Measurement Control” information message also includes IE “Measurement Identity.”
IE “Measurement Identity” is a reference number used by the network to identify a certain type of measurement. For example, the network may configure a Measurement Identity to be 1 to indicate measurement of a GSM system. The network may also configure a Measurement Identity to be 2 to indicate measurement of an LTE system. Measurement Identity configuration enables the network to manage different measurements. As an example, when the network determines that there is no need to measure the GSM system, the network may request the communication terminal to delete the Measurement Identity 1, so that the corresponding GSM measurement can be removed.
While IE “Measurement Identity” identifies the type of measurement, a network uses IE “Measurement Command” to manage the measurements performed by a communication terminal. IE “Measurement Command” can be configured as “Setup,” “Modify,” or “Release.” The “Setup” command is for setting up a new measurement. The “Modify” command is for modifying a previously defined measurement. The “Modify” command is equivalent to setting up a measurement based on an existing measurement identity, so that the network can modify some or all of the parameters of a measurement configuration corresponding to an existing IE “Measurement Identity.” As an example, through the “Modify” command, the network may request the communication terminal to delete one or more of the multiple measurement quantities that were originally configured. A measurement quantity is the quantity that a communication terminal measures on a measurement object, such as the signal strength of a neighboring cell or a network capacity. As another example, through the “Modify” command, the network may request the communication terminal to change the measurement reporting criteria, which trigger the measurement report. The “Release” command requests the communication terminal to stop a measurement and clear all information that is related to that measurement. Therefore, the “Release” command effectively deletes the measurement configuration. Similar to IE “Measurement Identity,” IE “Measurement Command” is also included in the “Measurement Control” information message.
As described above, the network sends the “Measurement Control” information message to the communication terminal to setup, modify, or release a measurement. Depending on the network configuration, however, the “Measurement Control” information message may or may not include IE “Idle Interval Information,” but must include IE “Measurement Identity.” For example, if the network configures IE “Inter-RAT measurement,” then it must configure a corresponding IE “Measurement Identity,” but the network need not configure IE “Idle Interval Information.” As another example, if the network does not configure an inter-RAT measurement, it may instead configure an intra-frequency measurement or intra-RAT inter-frequency measurement. In any case, the “Measurement Control” information message must include IE “Measurement Identity” to indicate the type of measurements, such as a GSM measurement, a TD-SCDMA measure, an LTE measurement, etc. But the “Measurement Control” information message may or may not include IE “inter-RAT measurement,” or IE “Idle Interval Information.”
While the measurement occasions configuration as described above may mitigate the inter-RAT measurement problem in a dual-mode terminal, it does not take into account different circumstances under which a communication terminal may perform measurements. As an example, the 3GPP protocol requests that a communicate terminal executes an inter-RAT measurement based on the configuration of IE “Idle Interval Information.” As described above, while the network that configures IE “Inter-RAT measurement” must configure the corresponding IE “Measurement Identity,” it may not configure IE “Idle Interval Information.” Without IE “Idle Interval Information,” the communication terminal may not have sufficient measurement occasions to perform the inter-RAT measurement.
As another example, the 3GPP protocol does not specify under what circumstances a configuration of IE “Idle Interval Information” is valid. For instance, it is unclear when a communication terminal can delete a measurement occasion that is configured in IE “Idle Interval Information.” In particular, a network may use the same measurement occasion configured in IE “Idle Interval Information” corresponding to different measurement identities and it is unclear whether the communication terminal can delete some of the same measurement occasions.
As yet another example, under the current 3GPP protocol, measurement occasions may also be wasted. For instance, a network may configure one-eighth of the idle interval for GSM measurements and one-fourth of the idle interval for LTE (including TDD-LTE or FDD-LTE or both) measurements. However, when a communication terminal has no neighboring LTE cell, the measurement occasions configured for the LTE measurements will be wasted. On the other hand, the measurement occasions configured for the GSM system may be insufficient, thus decreasing the performance of the GSM system measurement.
As yet another example, even if the measurement occasions are configured for inter-RAT measurements, decrease in data throughput may be unacceptable. For instance, according to the relevant communication protocols, when inter-RAT measurements are configured by using IE “Idle Interval Information,” the measurement occasions are configured to be 1 frame in every 4 or 8 frames. During those measurement occasions, the protocol requires that no data can be communicated. Thus, if the measurement occasions are configured using IE “idle interval information,” merely one type of inter-RAT measurement can result in a 25% or 12.5% loss (corresponding to 1 every 4 frames or 1 every 8 frames, respectively) of data traffic throughput.
If, in a communication terminal, more than two different radio access systems are present and are configured to use different idle intervals for measurements, then each inter-RAT measurement can result in a decrease of 25% or 12.5% in data throughput. In other words, if there is “N” number of different radio access systems, the total throughput loss can be 25%*N or 12.5% N. While the throughput loss may be reduced by increasing the measurement intervals or increasing the measurement quantities in the measurement occasions, these approaches may cause the measurement occasions to be insufficient for some measurements.
The above examples illustrate that the current inter-RAT measurement techniques often result in unreasonable configuration or allocation of measurement occasions, causing inefficient use or waste of the limited measurement occasion resources, poor measurement performance, low data traffic throughput, and increased time delays in data transmission. Therefore, there is a need for a method that efficiently and reasonably configures the measurement occasions and/or provides an improved measurement performance.